(1) Field of the Invention
The present invention relates to a double-side printing control method which is appropriate for an image forming apparatus having an integrated capability that enables the image forming apparatus to carry out one of copier, printer and facsimile functions.
(2) Description of the Related Art
As disclosed in Japanese Laid-Open Patent Application No.9-193481, a printing apparatus which carries out a double-side printing is known. The printing apparatus of the above publication is provided with a main page buffer and a count data memory. In the main page buffer, print data is expanded to image data and the image data is stored. In the count data memory, count data related to the print data is stored. When the double-side printing is carried out, the image data retained by the main page buffer is printed on both sides of each copy.
In the printing apparatus of the above publication, a secondary page buffer is provided in addition to the main page buffer and the count data memory. If the main page buffer lacks a capacity to store an amount of image data that exceeds an amount of image data corresponding to two pages during the double-side printing, the excess image data that is not stored in the main page buffer is temporarily stored in the secondary page buffer.
Alternatively, in the printing apparatus of the above publication, a receiving buffer may be provided in addition to the main page buffer and the count data memory. When print data is transmitted to the printing apparatus by a host computer, the print data is received at the receiving buffer and it is retained by the receiving buffer. If the main page buffer lacks a capacity to store an amount of image data exceeding the amount of image data corresponding to two pages during the double-side printing, the outputting of the excess image data to the main page buffer is delayed until the print data retained by the receiving buffer is expanded to image data.
In the above-described manner, the printing apparatus of the above publication makes it possible that the host computer transmit a double-side printing request to the printing apparatus without taking account of the internal construction of the printing apparatus. The printing apparatus of the above publication is intended to achieve an efficient, speedy double-side printing even when the printing apparatus is requested by the host computer to perform a double-side printing of plural copies.
Generally, when performing the double-side printing, it is necessary to hold an image memory area of a printing apparatus that stores image data the amount of which corresponds to two pages (or both sides of a copy). This enables the recovery of the image data when a paper jam or the like occurs in the printing apparatus during the printing of the image data for the front side of a copy. If the printing apparatus holds the image memory area during the double-side printing, the image data corresponding to two pages can be recovered by accessing the image memory area in such a case.
However, the amount of image data produced by the expansion of print data and stored in the image memory area varies depending on a given resolution of the print data sent by the host computer. When a certain resolution is set with the print data, the printing apparatus of the above publication may not hold the image memory area which store the image data the amount of which corresponds to two pages. If the printing apparatus of the above publication stores only an amount of image data corresponding to one page and a paper jam or the like occurs during the double-side printing, it is impossible to recover the image data corresponding to two pages by accessing the image memory area. Retransmission of the print data to the printing apparatus by the host computer is required to recover the image data corresponding to two pages.
Further, when performing an interleave printing, an alternate double-side printing of plural copies is performed for the front side of a first copy, the front side of a second copy, the back side of the first copy, the back side of the second copy, etc., in this sequence. On the other hand, when the normal double-side printing is performed by a conventional printing apparatus having an external storage part, print data for both sides of a first copy, print data for both sides of a second copy, etc., are sequentially expanded to image data and it is stored in the external storage part. The speed of the regular double-side printing (which depends on the speed of the expanding of the print data and the storing of the image data in the external storage part) by the conventional printing apparatus is not always higher than the speed of the interleave printing. In a case in which the speed of the regular double-side printing is lower than the speed of the interleave printing, it is difficult for the conventional printing apparatus to achieve an efficient, speedy printing.